Merge pull request #2151 from angelapwen/fix-cpu-group-bug

Account for existing but empty `cpus` file

CHANGELOG.md

@@ -6,7 +6,7 @@ Note that the only difference between `v2` and `v3` of the CodeQL Action is the
 
 ## [UNRELEASED]
 
-No user facing changes.
+- Fix an issue where an existing, but empty, `/sys/fs/cgroup/cpuset.cpus` file always resulted in a single-threaded run. [#2151](https://github.com/github/codeql-action/pull/2151)
 
 ## 3.24.3 - 15 Feb 2024
 

src/util.test.ts

@@ -449,3 +449,36 @@ for (const [
     versionStub.restore();
   });
 }
+
+test("getCgroupCpuCountFromCpus calculates the number of CPUs correctly", async (t) => {
+  await util.withTmpDir(async (tmpDir: string) => {
+    const testCpuFile = `${tmpDir}/cpus-file`;
+    fs.writeFileSync(testCpuFile, "1, 9-10\n", "utf-8");
+    t.deepEqual(
+      util.getCgroupCpuCountFromCpus(testCpuFile, getRunnerLogger(true)),
+      3,
+    );
+  });
+});
+
+test("getCgroupCpuCountFromCpus returns undefined if the CPU file doesn't exist", async (t) => {
+  await util.withTmpDir(async (tmpDir: string) => {
+    const testCpuFile = `${tmpDir}/cpus-file`;
+    t.false(fs.existsSync(testCpuFile));
+    t.deepEqual(
+      util.getCgroupCpuCountFromCpus(testCpuFile, getRunnerLogger(true)),
+      undefined,
+    );
+  });
+});
+
+test("getCgroupCpuCountFromCpus returns undefined if the CPU file exists but is empty", async (t) => {
+  await util.withTmpDir(async (tmpDir: string) => {
+    const testCpuFile = `${tmpDir}/cpus-file`;
+    fs.writeFileSync(testCpuFile, "\n", "utf-8");
+    t.deepEqual(
+      util.getCgroupCpuCountFromCpus(testCpuFile, getRunnerLogger(true)),
+      undefined,
+    );
+  });
+});

src/util.ts

@@ -440,7 +440,7 @@ function getCgroupCpuCountFromCpuMax(
 /**
  * Gets the number of available cores listed in the cgroup cpuset.cpus file at the given path.
  */
-function getCgroupCpuCountFromCpus(
+export function getCgroupCpuCountFromCpus(
   cpusFile: string,
   logger: Logger,
 ): number | undefined {
@@ -453,7 +453,10 @@ function getCgroupCpuCountFromCpus(
 
   let cpuCount = 0;
   // Comma-separated numbers and ranges, for eg. 0-1,3
-  const cpusString = fs.readFileSync(cpusFile, "utf-8");
+  const cpusString = fs.readFileSync(cpusFile, "utf-8").trim();
+  if (cpusString.length === 0) {
+    return undefined;
+  }
   for (const token of cpusString.split(",")) {
     if (!token.includes("-")) {
       // Not a range